1. Field of the Invention
The present invention relates to a novel copolymer comprising ethylene-.alpha.-olefin-branched conjugated polyvalent olefin, a composition containing the copolymer, a crosslinkable composition and a crosslinked copolymer composition, more particularly a crosslinkable composition having sufficient vulcanization rate without using an expensive diene monomer and, furthermore, a crosslinked copolymer composition obtained by crosslinking the crosslinkable copolymer composition, which is superior in heat deterioration resistance, weathering resistance, ozone resistance, chemical resistance and low-temperature characteristics, and a novel copolymer used therein.
2. Description of the Related Art
An ethylene-propylene-non-conjugated diene copolymer (EPDM) is superior in weathering resistance, ozone resistance and heat deterioration resistance because of no double bond in the backbone chain of the molecular structure, and it has hitherto been used exclusively in the usage to which the heat resistance and weathering resistance are required, e.g. weather stripping, door glass channel, radiator horse, waterproof sheet, antivibration engine mount, etc. by making the best use of its characteristics.
As is known to the public, EPDM is a crosslinkable copolymer obtained by copolymerizing an expensive non-conjugated diene monomer such as 5-ethylidne-2-norbornene, etc. with EPM (ethylene-propylene copolymer) which has no double bond in the backbone chain in the molecular structure and is not capable of performing the crosslinking reaction. Particularly considering the crosslinking rate and crosslinking density among practical characteristics, use of the expensive non-conjugated diene monomer was essential.
On the other hand, as a cheap conjugated polyvalent olefin, for example, there are conjugated monomers including 1,3-butadiene, isoprene, etc. It is known that some copolymers comprising ethylene and a conjugated diolefin, or propylene and the conjugated diolefin could be obtained by using a catalyst system containing vanadium which is known to be usefull for the industrial production of some kind of copolymers. However it is known that these techniques have a problem of causing a drastic decrease in activity or a drastic decrease in molecular weight of the polymer. On the other hand, a method of producing a copolymer comprising ethylene, an .alpha.-olefin and a conjugated diene, particularly branched conjugated polyvalent olefin (e.g. isoprene, etc.) and a copolymer having an uniform composition distribution of an .alpha.-olefin are not known.
Although a method for the production of copolymer comprising an olefin and a conjugated diene by using a catalyst system known as the industrially usefull one for the production of an olefin resin such as polyethylene, polypropylene, etc. and which also contains titanium compound and a magnesium compound as one component (Japanese Patent Kokai Publication No. 108008/1984) is laid open. As is apparent from the Examples of the method described in said patent, the resulting copolymer has broad molecular weight distribution and composition distribution (specifically, it means that a crystalline polymer and a non-crystalline polymer are simultaneously produced). For example, when the solution polymerization is carried out with the catalyst described above, clogging of piping was brought about by the insoluble polymer having high ethylene content which was formed during the polymerization reaction as byproduct, and this make the continuous production impossible. In addition, generally copolymer having broad composition distribution was applied to the many usage, for instance when used as the film, etc., however there arose a problem such as decrease in strength, increase in bleed component, stickiness caused by an increase of the extractable substance. Alternatively, when used as a low-density rubber, there arose a problem about practical physical properties, for example, it shows only poor physical characteristics such as compression permanent strain, tensile rigidity, etc. even after crosslinking.
On the other hand, recently high-molecular weight EPDM containing non-conjugated diolefin as a third component and which has low crystallinity and narrow molecular weight distribution/narrow composition distribution, which was produced by using a catalyst system comprising a transition metal compound and aluminoxane and also a method for the production process of the same in high efficiency (Japanese Patent Kokai Publication No. 64111/1990) have been suggested. Furthermore, as the copolymer using a conjugated diolefin as the raw material (Japanese Patent Kokai Publication No. 501633/1989), a crystalline copolymer having a cyclopentene ring structure on the backbone chain, which is derived from butadiene and ethylene using a specific metallocene catalyst, is also disclosed, but any information suggesting a method of producing a copolymer comprising an ethylene-.alpha.-olefin-branched conjugated polyvalent olefin having narrow molecular weight distribution/composition distribution, a copolymer obtained by the method, not to speak of the properties of the resulting copolymer and a crosslinked copolymer composition derived from said copolymer are not disclosed.
Under these circumstances, the present applicant has previously suggested a method of producing an olefin (co)polymer using a catalyst containing a transition metal complex having a specific ligand and, furthermore, a method of producing a copolymer of a high-molecular weight ethylene-.alpha.-olefin-diene using the catalyst (Japanese Patent Application No. 185081/1996). Thereafter, the present inventors have intensively studied. As a result, it has been found, that a copolymer of the ethylene-.alpha.-ethylene-branched conjugated polyvalent olefin (particularly a high-molecular weight ethylene-.alpha.-olefin-branched conjugated polyvalent olefin copolymer), which has never been obtained by using a conventional catalyst, is obtained by using the previously suggested catalyst. More in detail, it has been found that a high-molecular weight copolymer of ethylene-.alpha.-olefin-isoprene could be obtained and a crosslinkable copolymer composition comprising the copolymer and a crosslinking agent shows sufficient crosslinking rate in comparison with a crosslinkable copolymer composition produced by using a conventional expensive non-conjugated diolefin and, furthermore, a crosslinked copolymer composition shows superior stability for the deterioration by heating than conventional EPDM copolymer using expensive non-conjugated diene as third component. Thus, the present invention has been accomplished.